1. Field of the Invention
The present invention relates to a zinc oxide sintered compact and a method for producing the same.
2. Description of the Related Art
Oriented zinc oxide (ZnO) substrates having high transparency and high conductivity are expected to be substrates for optical devices including light emitting devices (such as light emitting diodes (LEDs) and surface light emitting devices), and optical devices (such as solar cells and light sensors). For example, Patent Document 1 (WO2014/092165) discloses a surface emitting device including an oriented zinc oxide substrate. A zinc oxide material, having both conductivity and light transmission can be subjected to ultrafine processing without electrical charge even by a focused ion beam (FIB) process, and is expected to be used as a functional device material constituting an optical MEMS which utilizes light transmission and optical characteristics of zinc oxide.
Zinc oxide sintered compacts containing Al to orient the (002) plane of ZnO have been disclosed (for example, Patent Document 2 (WO2010/114172), Patent Document 3 (JP5168726B1), Patent Document 4 (JP4595236B1), and Patent Document 5 (JP2010-80828A)). These documents, however, do not refer to transparency, while focusing on characteristics such as conductivity, Seebeck coefficient, and orientation with the intention of fabricating thermoelectric conversion elements. In these patent documents, oriented ZnO substrates are produced from only platy or spherical particles of ZnO by tape casting or orientation in the magnetic field.
Template grain growth (TGG) is known for producing an oriented sintered compact. In the TGG, template particles having shape anisotropy and matrix particles having equiaxiality are used to prepare a green compact such that the oriented template particles are dispersed in the matrix particles, and then the green compact is calcined to produce an oriented ceramic. For example, Non-Patent Document 1 (Matthew M. et. al., J. Am. Ceram. Soc., 80 [5], pp. 1181-1188 (1997)), Non-Patent Document 2 (Ender Suvaci et. al., J. Am. Ceram. Soc., 83 [8], pp. 2041-2048 (2000)), and Non-Patent Document 3 (Yunfei Chang et. al., J. Am. Ceram. Soc., 96 [5], pp. 1391-1397 (2013)) disclose the production of oriented alumina sintered bodies by TGG. Furthermore, Non-Patent Document 4 (Ender Suvaci et. al., J. Euro. Ceram. Soc., 25, pp. 1663-1673 (2005)) discloses the production of an oriented zinc oxide sintered compact by TGG.